Allow all warnings from Kestrel to be bubbled in the AppHost

See the conversation here:

> We suppressed that because we wanted to tightly control what was being output to the console. For example if you raise it to warning you get this in the output:
>
> 

@adityamandaleeka @amcasey @halter73 - would it make sense to have a setting in Kestrel that told it "I did this override intentionally, please don't emit a warning for this?" That way Aspire wouldn't need to suppress all warnings, and then opt back in case-by-case to the warnings it wants to bubble out.

_Originally posted by @eerhardt in https://github.com/dotnet/aspire/issues/2914#issuecomment-2022991797_

We should follow the suggestion of clearing out the `ASPNETCORE_URLS` env var and continue allowing all Kestrel warnings to be bubbled up to the user. See also

* https://github.com/dotnet/aspire/pull/1933
* https://github.com/dotnet/aspire/pull/3212